How do I combine 2 garmin accounts (accidentally set up with 2 different emails)?

You can export your activities from one account and import them into the other account.

While you can export your daily monitoring files, I know of no way to import them.

I want to do the same thing...

did you end up being able to merge your two Garmin Connect accounts? I have the same problem and all the reddit threads are blocked for some reason

Get the full data dump from the unwanted account at Garmin International | Account | Data Management | Data Export and then drop the unzipped files to the account you want to keep: https://connect.garmin.com/modern/import-data 

i've managed to extract the data from one account, however, when i attempt to import the download utilizing the import data function, i receive a "We don't support the file type you tried to import" error.  is there only one specific folder from the initial extract i need to import?

Try uploading all files. No folders, no zip archives. You won't be able to import all, but those files that can be imported, will pass without an error.